Deer mice are the principal reservoir hosts of Sin Nombre virus, which causes the great majority of hantavirus cardiopulmonary syndrome cases in North America. Unlike human infections, which are fatal in about a third of the cases, infected deer mice do no exhibit symptoms of disease and remain otherwise healthy but persistently infected, probably for life. This project has focused on understanding the immunological events that lead to persistent infection without disease. Our efforts have demonstrated that an anti-inflammatory immune response appears to predominate at persistence and this response likely limits pathology, but also compromises viral clearance. Andes virus also infects deer mice; however, it is cleared without disease. The project will continue to examine how SNV evades the host response and why Andes virus is cleared by focusing on the genetic, molecular and cellular events during the host response to these viruses.